AFORS-HET-based numerical exploration of tunnel oxide passivated contact solar cells incorporating n- and p-type silicon substrates

The development of a tunnel oxide interfacial layer capped by a highly doped poly-Si layer is considered one of the most promising methods to reduce charge carrier recombination and improve the performance of conventional PERC devices. The thickness and doping concentration of emitters and BSF layers greatly influence the tunnelling current in TOPCon devices. In this research, we evaluated the performance of tunnel oxide passivated contact (TOPCon) solar cells by conducting an in-depth analysis of various key parameters. The parameter include the type of silicon substrate (n or p-type); the thickness and doping density (Na/Nd) of n, n+, p, and p+ layers; and surface recombination velocity (front/rear), which were analyzed using AFORS-HET simulation software. A comparative analysis of performance demonstrates that the highest efficiency is achieved in the n-TOPCon solar cell with the following values: Voc = 660.2 mV, Jsc = 45.05 mA cm−2, FF = 82.87%, and PCE = 25.74%. In the optimized p-TOPCon solar cell, the open circuit voltage (Voc) and fill factor (FF) exhibit improvements of 35.9 mV and 0.39%, respectively. However, the values of Jsc and PCE decrease by 6.44 mA cm−2 and 2.2%, respectively, in p-TOPCon solar cells. Furthermore, photo-electroluminescence analysis reveals that the n-TOPCon solar cells exhibit a higher maximum photon flux (front/rear) than p-TOPCon solar cells.


Introduction
The silicon solar cells with a TOPCon structure are currently dominating the PV industry, according to report by ITRPV.However, the aluminum back surface eld (AlBSF) technology is likely to cease aer 2025.TOPCon silicon devices are considered innovative and are expected to eventually replace passivated emitter and rear cell (PERC) ideas in the future 1 owing to their greater open circuit voltage (V oc ) and higher ll factor.Presently, silicon devices with a tunnel oxide passivated contact cell (TOPCon) structure exhibit exceptional potential and have attracted considerable interest.This innovative idea avoids the somewhat complex process for localized contacts and provides the advantage of full-area contact. 2 It is compatible with the current manufacturing line and high-temperature process conditions.In solar cells, a thin oxide layer is employed to offer complete-area passivation of greater quality, as well as an electron tunnelling function on the rear surface of the silicon wafer.][5] Despite a di-electric layer that passivates the rear side of a silicon passivated emitter and rear cell devices, recombination at the interface between the metal and silicon still occurs. 6,7In industrial PERC devices, which possess a performance of 22.21%, the current density of the recombination at the rear metal contact has been measured at 660 fA cm −2 . 8,9Moreover, the contact geometry on the rear side of the PERC design, which is locally patterned, introduces 3D charge carrier transport.4][15] LID is an ordinary process that leads to efficiency degradation of crystalline silicon solar cells.LID degrades rather quickly and can reach saturation in a few days.In recent years, the photovoltaic world has become aware of a new phenomenon causing crystalline silicon solar cells to degrade.It can be found in PERC solar cells made of monocrystalline and multi-crystalline silicon (mc-Si).This process is termed light and LeTID.The light-induced degradation process reaches saturation in a short period of time at the normal temperature,

RSC Advances
PAPER while LeTID requires high temperatures for a longer duration to reach saturation.7][18] Currently, PERC solar cells lead the market, and LeTID can cause up to 16-17% performance loss in the PERC solar cells.Consequently, the study on light and LeTID is substantial.The results from the study of Bredemeier et al. demonstrate a relationship between the silicon wafer thickness and the degree of LeTID deterioration.The results obtained by Bredemeier et al. demonstrate that the degradation degree of LeTID is linked to the thickness of the silicon (Si) wafer.A Si substrate with less than 120 mm thickness does not suffer much degradation. 19,20n the TOPCon structure, charge carriers pass through insulators by a quantum tunneling process that passivates wafer and also reduces the recombination losses.The same apparatus that is used for the fabrication of PERC solar cells can also be used for manufacturing the TOPCon structure. 21,22The manufacturing of the TOPCon structure is more straightforward than that of the PERC solar cells, as there is complete passivation and metal contact at the rear side.During the fabrication route of TOPCon devices, thin layers of tunnel oxide and highly doped polycrystalline-silicon (poly-Si) are deposited, effectively minimizing the charge carrier recombination. 23,24he TOPCon structure has signicant potential to penetrate the global market.The TOPCon solar cells offer several advantages over the traditional PERC solar cells, one of which is the presence of one-dimensional (1D) carrier ow facilitated via tunnelling through the oxide layer.In TOPCon structures, the silicon wafer is not directly in contact with the back metal but is parted by polysilicon and SiO x layers.Highly efficient crystalline silicon solar cells have the tunnel oxide passivated contacts at the rear side to prevent recombination.The TOPCon solar cell, which stands for Tunnel Oxide Passivating Contact, operates under the assumption that carrier transport occurs via quantum tunneling through an ultrathin SiO x layer (<2.0 nm).Despite rapid improvements in the TOPCon cell efficiency, some basic device physics remains poorly understood.SiO 2 has long served as an insulating di-electric layer in thin-lm transistors used in displays due to its well-known properties as a perfect insulator.However, photo-generated carriers in TOPCon solar cells must transport through an insulating SiO x layer, and the transport mechanism is logically assumed to be tunnelling.
Another signicant benet is the superior carrier selectivity provided by the SiO x layer.It achieves this by enabling dri currents of only one type of charge carrier via quantum mechanical tunnelling, thereby reducing minority charge carrier recombination at back contact. 23,25The thin oxide layer in TOPCon solar cells allows for efficient electron/hole transfer, depending on the conductivity of the substrates.This is due to dangling bonds, which are chemical bonds connected to atoms in the solid's surface layer that extend outward rather than joining with other atoms, on the top surface of the single crystal.The utilization of highly doped polysilicon, with its high conductivity, helps reduce junction resistance and enhance current output. 26These layer properties show crucial parts in cell design, aiming to achieve high V oc , greater efficiency and ll factor, all of which are promised by the TOPCon structure.
The effective growth of the TOPCon conguration hinges on four crucial steps: (1) the creation of an ultra-thin SiO x layer, (2) the growth of a highly doped amorphous silicon onto SiO x as the above-mentioned layer, (3) thermal annealing at high temperatures to activate dopants and crystallize the doped amorphous silicon layer, resulting in a multi-crystalline structure, and (4) subsequent hydrogenation handling aer annealing to diminish defect states within the doped polycrystalline silicon layer. 27Therefore, it becomes evident that advancing and optimizing each of these treating steps can enable the production of high-performance TOPCon devices compared to the PERC conguration.
TOPCon devices are considered to be the next-generation technology for enhancing the performance of industrial silicon devices.The initial proposal for the structure of the TOPCon devices was made by Feldmann et al. in 2013, where a 10 × 10 cm 2 cell achieved an efficiency of 22.9%. 28The recombination rate refers to the loss of generated charge carriers and mainly occurs in the surface and bulk areas of the device.The rear di-electric or passivated contact reduces recombination. 29Several parameters inuence recombination, including effective minority charge carrier lifetime (s eff ), emitter recombination current (J oe ), and surface recombination velocity (SRV).High SRV results in the formation of a dead layer when the SRV increases, with the carrier recombining at the defect surface owing to fewer minority carriers' lifetime and the diffusion length.The SRV is a crucial variable signicantly affecting the efficiency of the devices.The SRV and the dead layer also impact the supplementary parameters of the cell, such as J sc and I sc .The effective lifetime is determined by both the surface lifetime (s s ) and bulk lifetime (s b ), and their relationship can be explained using the following equation: Effective charge carrier lifetime can be demonstrated as a function of SRV using the following equation: In these equations, W denotes the thickness of the silicon wafer and D denotes the diffusion constant of the minority carriers.The efficiency of p-TOPCon cells was investigated by Quokka simulations, where variations in bulk lifetime (s b ), r (resistivity), and carrier discrimination of the polycrystalline silicon passivated contact were examined. 30Reducing surface charge recombination losses is fundamental to achieving enhanced efficiency in commercial solar cells.In the absence of illumination, the emitter recombination current surpasses the base recombination current.This is primarily attributed to the high defect density in the majority section, energy-band gap reduction, and the Auger recombination route. 31raunhofer ISE has recorded a record efficiency of 25.7% for these cells.Most studies on TOPCon structure solar cells have focused on utilizing SiO 2 as the tunnelling layer on the n-type silicon wafers owing to its outstanding passivation properties for the n-type silicon interface.Moreover, marketable solar cells currently rely mainly on the p-type PERC structure.Transitioning from the p-PERC conguration to the p-TOPCon conguration necessitates a different di-electric layer for the tunnelling oxide layer.Nevertheless, the average stabilized performance of large-area n-TOPCon devices in mass fabrication has been found to exceed that of the prevailing p-PERC devices in the market. 32everal theoretical simulation works have explored using SiO 2 /polycrystalline silicon passivation contacts at the rear for p-TOPCon cells in the last few years.TCAD simulations have examined the impact of tunnelling oxide thickness and bulk properties on p-TOPCon cell performance. 33Gao et al. reported a simulation study of a 22.40% p-TOPCon structure using the Quokka soware with industrial-grade process parameters. 34A logical, numerical study is mandatory for a deeper knowledge of signicant factors that inuence how well the devices perform.These fundamental characteristics are the quality and thickness of the wafer, BSF, emitter layer, the quality of the n + -Si layer and doping concentration.Steinkempe et al. has provided a useful example for numerical simulation to determine the performances of the TOPCon solar cells with several n + -Si materials. 35,36n this work, we studied the performance of TOPCon devices using both n-and p-type Si wafers.We varied the thickness of the emitter, substrate, and back surface eld layers, as well as the doping density of the emitter/base/rear side (N a /N d ) and the SRV.We aimed to optimize these parameters and achieve high efficiency for both n-& p-type TOPCon structures.We also assessed the impact of these parameters on the front and rear photon ux (measured in m −2 S −1 ) using the AFORS-HET simulation soware. 37llows for changes in any external quantity.Furthermore, the soware considers various physical processes of silicon devices, such as recombination, generation, transportation, and contact. 38AFORS-HET mathematically explains semiconductor eqn (3)-( 5) and the suitable boundary limitation in one dimension.

Simulation methodology
where D is the displacement eld, n and p are the electron and hole densities, r is the net charge of all the traps positioned in the band gap, and N a and N d are the acceptor and donor densities.The electron and hole current densities are also indicated as J n and J p, respectively.G represents the optical generation rate, while R n and R p correspond to electron and hole recombination rates.Various recombination processes such as Auger recombination, direct band-to-band recombination, and the Shockley-Read-Hall recombination can be employed to model recombination phenomena. 39The electron and hole pair creation can be explained by considering the Lambert-Beer absorption or coherent and incoherent multiple reections.Interface currents are modelled using either thermionic emission or dri-diffusion.Various models can represent metallic inter contacts, such as metal/insulator/ semiconductor contacts or Schottky or Schottky Bardeen semiconductor/metal contacts. 40Many simulation articles have been published using AFORS-HET, which has gained widespread acceptance as a tool for understanding Si-heterojunction solar cells.The default parameters for optical and electrical layers optimized in this research are based on previously published works. 28The conguration of the n-TOPCon device used in this study is as follows: front electrode/SiN x /p + -Si/n-Si wafer/ SiO 2 /n + -Si/back electrode.For the p-TOPCon device, the structure is as follows: front electrode/SiN x /n + -Si emitter/p-Si wafer/ SiO 2 /p + -Si/back electrode. 41The input initial parameters used for the simulations can be found in Tables 1 and 2 for the n and p-TOPCon devices, respectively, and all optimization is carried out with the thickness of the tunnel oxide SiO 2 layer at 1 nm for both n/p TOPCon solar cells.
In the equations provided, t = thickness, N a is the acceptor concentration, N d is the donor concentration, Chi is the electron affinity energy, E g is the energy band gap, d k is the relative di-electric constant, m e is the relative effective mass of the electron, m h is the relative effective mass of the hole, and D ph is the pinhole density through insulator layers.

Results and discussion
To determine the device efficiency with different optimized parameters, The performance and photo-electroluminescence (m −2 S −1 ) of TOPCon structures were studied incorporating nand p-Si substrates.The optimization of primary factors, First, heavily doped n + poly-Si creates an accumulation layer at the absorber surface due to the work function difference between the n + poly-Si and the n-Si absorber.This accumulation layer or band bending provides a barrier for holes to get to the tunnel oxide, while electrons can migrate easily to the oxide/Si interface that is favorable for the lesser barrier height of oxides at the conduction band as well as lesser electron effective mass at the SiO 2 layer.Fig. 2b shows the p-Si/SiO 2 /p + -poly-Si structure in p-type TOPCon solar cells, featuring a lower valence band offset (DE v ) and a higher conduction band offset (DE c ) between p-Si and p + -poly-Si.This conguration facilitates hole collection on the heavily doped p + -poly-Si side.
Path towards cell parameter optimization (n/p TOPCon solar cells) The optimization of layers (thickness, doping concentration, and FSRV/RSRV) in the n-TOPCon solar cell was started from the silicon substrate layer.Then BSF and emitter layers were optimized gradually.The layer thickness/doping concentration optimization sequence is as follows: n-Si substrate, n + Si layer, p + Si layer, FSRV and then RSRV of the n-TOPCon structure, as given in Table 3.However, for p-TOPCon, it is p-type c-Si, p + -type Si layer, n + -type Si layer, FSRV and RSRV, respectively, as given in Table 4.

Optimization of n-TOPCon solar cells
At rst, the silicon wafer thickness of the n-TOPCon solar cell was optimized by varying it from 150 to 210 mm, as presented in Fig. 3.A maximum efficiency of 14.15% observed at 150 mm reduction in wafer thickness will reduce the recombination sites, hence 150 mm was chosen as the standard wafer thickness.
It was obvious that the FF and Con.efficiency decreased with the increase in n-Si wafer thickness.The results revealed that J sc , V oc , FF and h negatively correlated with the substrate thickness.Then the doping concentration of 150 mm-thick n-Si wafer was changed from 5 × 10 12 to 5 × 10 17 cm −3 .A 0.83% increase in the efficiency of n-TOPCon was observed at a doping concentration of 5 × 10 17 cm −3 for the n-Si substrate.The bulk doping level signicantly affects bulk recombination in waferbased TOPCon cells, as high doping levels control the minority carrier lifetime.Therefore, optimizing both the bulk doping level and wafer thickness is crucial for enhancing overall cell performance.An increase in V oc (mV) and FF (%) and a decrease in J sc (mA cm −2 ) were also observed in this case, as shown in Fig. 4. By using the optimized values of the n-Si wafer (thickness and doping concentration), the thickness of the BSF layer (n + Si) was varied from 2 to 30 nm.It was observed that the efficiency increased by 0.04% with the increase in other output parameters at 2 nm thickness of the n + Si BSF layer, as shown in Fig. 3.
The optimized doping concentration of BSF (n + silicon) was observed as 10 × 10 20 cm −3 with the above-stated optimized  parameters, as shown in Fig. 4. The result showed a certain increase in efficiency by +7.24%, as higher doping concentrations in the polysilicon layer reduce the series resistance of the cell.This improved conductivity allows for more efficient carrier transport reducing resistive losses and thus enhancing the ll factor and overall efficiency of the cell along with the increase in J sc and FF of n-TOPCon.An increase in J sc and efficiency with the increase in BSF doping concentration is due to a low recombination current.The increase in V oc is also due to the additional built-in voltage that is produced by the BSF layer, so the V oc value increases with the increase in doping value and the generation of electric eld on the back surface of the cell, and minority charge carriers generated near the surface escape from the recombination process by this electric eld. 42y using the above-optimized parameters and the thickness variation of the p + Si emitter layer from 0.1 to 0.9 mm, an increase in efficiency by +2.19% was observed for 0.1 mm p + emitter thickness, as illustrated in Fig. 3.The doping concentration (p + Si emitter layer) of 5 × 10 17 showed a rise of +0.93% in efficiency along with the increase in V oc and FF of simulated n-TOPCon devices, as shown in Fig. 4. The open circuit voltage of the cell, V oc , increased with the increase in the doping density in p + Si, but short circuit current density, J sc , started to decrease.With the increase in doping density in p + Si, the built-in potential increases, and the open-circuit voltage is related to the built-in potential and the quasi-Fermi levels.As the doping concentration increases, the built-in potential increases, which directly enhances V oc ; meanwhile, the short circuit current density J sc decreases.However, substantial excessive doping can also increase the recombination loss in the emitter region, increasing the recombination loss of light-induced carriers and reducing the number of free carriers available to contribute to the short-circuit current with decreased J sc . 43Therefore, the efficiency of the cell exhibited a maximum value at 1 × 10 17 cm −3 . 44The effects of front and rear SRV were also investigated in this work, as shown in Fig. 5.At rst, we used a xed rear SRV of 1 × 10 5 cm s −1 and varied the front SRV from 1 × 10 1 to 1 × 10 8 cm s −1 .The results showed the stable and maximum output parameters of n-TOPCon solar cells for 100 cm s −1 front SRV.However, the increase in front SRV decreased the J sc , FF and efficiency.Then by using 100 cm s −1 as the front SRV, the rear SRV was varied from 1 × 10 1 to 1 × 10 8 cm s −1 .The result showed that the maximum J sc , FF and efficiency of n-TOPCon were observed at 1 × 10 4 cm s −1 rear the SRV with 1 nm oxide thickness.However, the output parameters of the n-TOPCon device decreased with the increase in the front SRV but not much affected by the rear SRV, and it has been proved that an oxide of 1.0 nm thickness is sufficient to keep the V oc and J sc stable even when the rear SRV reaches 1 × 10 7 cm s −1 and this might be because the oxide suppresses the leakage current, 3,45 as depicted in Fig. 5. Simulation outcomes demonstrate that the conversion efficiency of silicon-based n TOPCon solar cells decreases as the SRV value increases owing to a larger recombination rate of the minority carriers near the front surface of the solar cell.The SRV leads to carriers that produce a loss added to the potential current or voltage of the cell as most of the recombination occurs in the majority and surface region, and a dead layer is produced due to the high SRV. 3 Higher  Paper RSC Advances surface recombination velocity causes a decrease in the rate of photo-generated charge carriers.The detailed optimization effect of the n-TOPCon device is given in Table 3.

Optimization of the p-TOPCon solar cell
Improvement of TOPCon conguration using p-type silicon wafers, similar to the p-PERC solar cell, is an appealing approach in photovoltaics.In the p-TOPCon structure, the emitter is made of n-type silicon that exhibits better surface properties than p-type silicon.Therefore, it is positioned at the front of the cell where most light is absorbed.Consequently, adopting the approach of having the top of the cell as the negative terminal and the rear as the positive terminal proves to be advantageous in p-TOPCon devices.In this work, we optimized the p-Si wafer thickness by varying it from 100 to 210 mm and selected it as 100 mm.The performance of p-TOPCon was 13.15% and J sc was 33.77 mA cm −2 , as depicted in Fig. 6.The Con. Efficiency and FF were found as maximum at this thickness, whereas all other output parameters were almost constant.The nal photocurrent and overall cell performance depend highly on the silicon wafer's thickness.Although the cost is reduced when the thickness decreases, the production line's yield also decreases.One benet of going thinner is that the lifetime does not become an issue; the thinner the layer, the lesser the possibility for carrier recombination.Then, using a 100 mm p-Si wafer, its doping concentration varied from 1 × 10 14 to 9 × 10 18 .The doping density essentially affects the performance of solar cells.The reverse saturation current reduces with the increase in the doping density, enhancing V oc and PCE.This improvement is continued until high doping effects begin to appear.Maximum doping levels affect the lessening of bandgap and minority charge carrier lifetime.Both cause the reverse I sc to decrease again aer reaching a peak with a doping density in the substrate.An increase of +5.43% in p-TOPCon efficiency was observed at 2 × 10 18 cm −3 doping concentration (p-Si wafer) along with the increase in V oc and FF, as shown in Fig. 7.We used the above-optimized parameters and varied the thickness of the BSF (p + type silicon) layer from 5 to 50 nm, as shown in Fig. 6.Maximum efficiency with no increase in other parameters as compared to the earlier result was obtained at 25 nm.By producing a p + layer under metallization, a back surface eld is achieved.This layer reects the Fig. 3 Effect of the thickness of n-Si, n + -Si and p + -Si on the V oc , J sc , FF, efficiency and con.efficiency of the n-TOPCon device.
minority carrier electrons and stops them from reaching the highly recombining metal-silicon contact, decreasing the minority carrier recombination, which essentially improves efficiency.By using 25 nm as the optimized thickness of p + Si, its doping concentration was varied from 2 × 10 15 to 9 × 10 20 cm −3 , as shown in Fig. 7.An increase of +1.42% in efficiency was observed at 4.1 × 10 20 cm −3 with the increase in J sc and FF.The back surface eld (BSF) can be created by introducing a highly doped p + -Si layer near the rear surface of p-type bulk.As the acceptor doping level or the hole density increases, the energy of conduction and valence electrons also increases.This generates an electrical eld (BSF) that pushes electrons towards bulk and attracts holes into the BSF area.This leads to better separation of electrons and holes close to the rear surface, reducing the electron-hole recombination and improving the overall efficiency. 46y using the above-optimized parameters, the thickness of the n + Si emitter layer was varied from 0.1 to 2 mm, as shown in Fig. 6.A prominent increase of 2.93% in the efficiency of p-TOPCon solar cells was observed at 0.1 mm thickness of the n + Si emitter layer because by making the front layer exceedingly thin, a signicant portion of the carriers produced by the incoming light are absorbed near the front surface.Then the doping density of the n + emitter layer was varied from 1 × 10 15 to 9 × 10 21 cm −3 by using the above-optimized parameters, as depicted in Fig. 7.An ideal emitter conguration aims to minimize the (i) recombination losses in the diffused region also at the surface of the cell and (ii) resistive losses as the emitter doping prole signicantly affects the device characteristics of the solar cell. 47The performance of the p-TOPCon device was increased by 0.58% at 2 × 10 18 cm −3 doping concentration (n + -Si) of the emitter layer that reduces reverse saturation current, thereby increasing the open circuit voltage.The I-V results show that V oc and J sc are intensely affected by FSRV and show no effects by changing the BSRV on P-TOPCon solar cells, as shown in Fig. 8, because carrier-selective connections are used in TOPCon cells to permit the electrons to ow through while blocking the holes.This selective transport mechanism reduces the recombination of minority carriers at the rear surface, thereby minimizing the effect of rear SRV on cell performance. 48y changing the FSRV both V oc and J sc decrease with the increase in SRV.A reduction in J sc and V oc is noticed only due to intense carrier recombination close to the front surface of the cells, which signicantly lowers cell performance.Optimized front and rear SRVs are found as 100 cm s −1 and 10 000 cm s −1 , respectively, with an improved efficiency of 23.54% of p-TOPCon devices.
The comparison of n-TOPCon and p-TOPCon showed a substantial increase in V oc and FF of p-TOPCon devices.However, the efficiency and J sc of n-TOPCon were higher than those of the p-TOPCon device.
Tables 3 and 4 show that the performance of the n/p TOPCon structure has gradually improved with the optimization of the thickness and doping density of all layers.

Photo electroluminescence of n/p TOPCon
Photoluminescence (PL) refers to light emission from a material when it is optically excited.When a material is exposed to light with sufficient energy, it absorbs photons and undergoes electronic excitations.Ultimately, these excitations relax and electrons return to their ground state.If this relaxation process involves light's radiative emission, it is known as photoluminescence.The nature of optical excitation plays a vital role in PL.The energy of excitation determines the initial photoexcited state and inuences the depth to which the incident light can penetrate the material. 49The photon ux plays a crucial role in determining the number of generated electrons and, consequently, the current produced by solar cells.However, the photon ux alone does not provide information about the energy or wavelength of photons.Therefore, it is necessary to specify the energy or wavelength of photons in the light source.Combining the photon wavelength or energy with the corresponding photon ux can calculate the power density for the photons at particular wavelengths.Fig. 9 and 10 show the photoluminescence (PL) results for the n/p TOPCon solar cells.The gure and wafer thickness show a straight line in the PL spectrum.However, the actual intensity of the wafer spectrum is low as compared to the other parameters of the cell, as shown in the spectrum of the adjacent gure for both n/p TOPCon.

Photo electroluminescence of n-TOPCon
The PEL results show a relation between the wavelength of the emitted light and the photon ux (m −2 S −1 ).Emission at longer wavelengths represents the transition of electrons with lower energy levels and vice versa.The photon ux is important in calculating the number of generated electrons and the current

Conclusion
This study used the AFORS-HET numerical simulator to simulate TOPCon devices with n-and p-type silicon substrates.We aimed to optimize the device parameters and achieve a PCE of more than 25% in n-TOPCon cells and more than 23% in p-TOPCon cells.We optimized various parameters including layer thickness (Si-substrate, emitter, BSF), acceptor and donor doping concentrations (N a /N d ), and the front and rear SRV.We optimized a doping concentration of 5 × 10 17 cm −3 for the p +type Si layer (0.1 mm), and obtained the following results for the n-TOPCon cell: V oc = 660.2mV, J sc = 45.05 mA cm −2 , FF = 82.87%,and PCE = 25.74%.A comparison between n-TOPCon and p-TOPCon cells revealed a signicant increase in the V oc and FF for the p-TOPCon cell.However, the efficiency and J sc of the n-TOPCon cell were higher than those of the p-TOPCon cell.Furthermore, the maximum photon ux was observed in the n-TOPCon cell compared to the p-TOPCon cell.Photo electroluminescence (PEL) has direct effects on the power generation Maximum output power increases with the maximum photon that falls on the cell and also increases the number of electrons produced; hence, more current is produced from solar cells.This theoretical research provides a foundation for developing efficient p-TOPCon solar cells with maximum performance, opening up new avenues for further advancements in this eld.

Fig. 1
Fig. 1 displays the schematic diagram of the n-and p-type TOPCon solar cell simulated using AFORS-HET.AFORS-HET employs nite differences to solve one-dimensional 1D semiconductor equations under various conditions, including Poisson's and electron and hole transport equations.These conditions include the following: (a) equilibrium mode to describe a semiconductor device numerically; (b) steady-state mode; (c) steady-state mode with minor sinusoidal perturbations; (d) basic transient mode, where external quantities are instantly turned on or off; and (e) general transient mode, which

Fig. 1
Fig. 1 Simulated structure of (a) n-type and (b) p-type TOPCon devices.

Fig. 2
Fig. 2 Energy band diagram showing the rear side of (a) n-TOPCon solar cells and (b) p-TOPCon solar cells.

Fig. 4 Fig. 5
Fig.4Effect of the doping concentration of n-Si, n + -Si and p + -Si on the V oc , J sc , FF, efficiency and con.efficiency of the n-TOPCon device.

Fig. 6 Fig. 7
Fig.6Effect of the thickness of p-Si, p + -Si and n + -Si on the V oc , J sc , FF, efficiency and Con.efficiency of the p-TOPCon device.

Fig. 8
Fig.8Effect of the front and rear SRV on the efficiency of the p-TOPCon device.

Fig. 9 (
Fig. 9 (A and B) Photon flux at the front and back sides of the n-TOPCon device.

Fig. 10 (
Fig. 10 (C and D) Photon flux at the front and back sides of p-TOPCon devices.

Table 1
Input device parameters used for the simulation of the n-TOPCon solar cells Boundary of the front contact Texture surface (54.75°), fat band, absorption loss Front metal contact MS Schottky contact model, SRV = 10 2 cm s −1 p + -type silicon layer t = 0.1 mm, lifetime setting: 1 ms, N a

Table 4
Simulated p-TOPCon solar cells